The present invention relates to monolithic refractories such as casting material, gunning material, burning type hot repairing mix, mortar, tamping material, ramming material or the like to be used as lining or repairing material for various furnaces, molten-metal vessels used in pig-iron or steel making process.
In recent years, with increasing severity of operating conditions in pig-iron and steel making industries, as monolithic refractory to be used as lining material or repairing material for a variety of molten-metal vessels such as a converter, a ladle, a torpedo-car or the like, there have generally been used carbon-bonded materials having superior corrosion resistance and spalling resistance.
This is because the conventional materials using sodium phosphate or sodium silicate have the drawback in strength that these materials when penetrated by slag generate a low-melting point compound which causes melting and damage of the materials. In order to cope with this, there have been proposed a method directly using bonding agents such as alumina cement, sodium phosphate or sodium silicate with addition of graphite or coke thereto and a further method using these bonding materials in combination with tar or pitch to form carbon bond.
In the case of burning type hot repairing mix, there is also known a method using tar or pitch alone as bonding material. Also, there has been developed a further method of using phenol resin in order to render a period needed for obtaining bonding strength shorter than that needed when using tar or pitch.
In the case of monolithic refractory using tar or pitch, when this is used as casting material for example, a great amount of volatile component emits from the tar or pitch when the temperature is raised at the time of its application, whereby there occur rupture and environmental problem as well. For this reason, it is difficult to use these materials by a large amount, so that it has not been possible to cause the material to sufficiently provide its effect of preventing slag penetration which is an advantage of the carbonaceous material. Also, when used as gunning material, it requires use water on its application. Then, after evaporation of the water, pitch is once melted and then produces the carbon bond. However, in the case of the ordinary pitch, the pitch has low viscosity at the time of its melting. So that, when the pitch is added by a certain amount, there occurs such problem as deformation or sagging. Therefore, in this case too, it has not been possible to add a large amount of pitch. Further, in the case of burning type hot repairing mix, there are two types, i.e. one which hardens after flows on its introduction and the other which hardens immediately when introduced. In the case of the former type which hardens after flows, it is necessary to use pitch having a low softening point. This inevitably leads to low residual carbon, so that the material cannot provide sufficient hot strength or adhering strength. On the other hand, in the case of the latter type which hardens immediately at the time of its introduction, this type is intended to be applied to a sloped surface. Thus, this material must be hardened at the position of its introduction. However, in the case of the ordinary pitch or tar, when added by a necessary amount, the pitch or tar, because of its low viscosity, sags from the position of introduction, so that it cannot be applied to the target position.
On the other hand, in the case of monolithic refractory using phenol resin, if used as repairing material, it provides the advantage of shorter time required of the material to provide the bonding strength in comparison with tar or pitch. But, this material has drawbacks of significant shrinkage occurring in the applied material and weak bonding strength.
For the above-described reasons, there has been a demand for improved monolithic refractory which is superior in both applicability and durability by solving the drawbacks of the conventional monolithic refractories using carbon bond such as rupture, lack of volume stability, low adhesive strength, low hot strength and so on.